The present invention relates to a detector for detecting discontinuities in a medium to be researched, particularly though not exclusively, for detecting discontinuities inside metal pipes as at joints.
It is desirable to be able to detect joints in gas mains since these can leak. This has become a particular problem since the replacement of manufactured gas by natural gas. The latter is much drier than the former, which can and does lead to joint packings drying out, shrinking and then leaking.
A present proposal for detecting joints in cast iron gas mains is to insert through the main a radio transmitter and to follow the transmitter above ground with a receiver. Reception of a signal indicates a joint.